One of the most profound questions in planetary science is how Venus, a planet believed to have once resembled Earth, evolved into the inhospitable world it is today. The key to unraveling this mystery lies in understanding the significant difference in water content between Venus and Earth. New research has shed light on this puzzle, pointing to a process called dissociative recombination as the culprit behind Venus’ water loss.
Venus and Earth share many similarities in terms of size, mass, and composition, yet they couldn’t be more different in terms of habitability. While Earth is a thriving oasis teeming with life, Venus is a hellish inferno with temperatures hot enough to melt lead. The toxic carbon dioxide clouds and sulfuric acid rain on Venus make it inhospitable to any form of life. This stark contrast between the two planets has long perplexed scientists, especially considering that Venus should have had a similar amount of water to Earth during its formation billions of years ago.
Models of water loss from Venus have failed to account for the vast difference in water content between Venus and Earth. To put things into perspective, if Earth’s water were spread evenly over its surface, it would create a global ocean three kilometers deep, whereas Venus has a global equivalent layer of water just three centimeters deep. Previous theories on Venus’ water loss could not explain this discrepancy until the recent discovery of dissociative recombination.
Scientists have long overlooked the role of dissociative recombination, a process that causes hydrogen to escape into space from Venus’ atmosphere. This phenomenon, facilitated by the recombination of a molecule called HCO+, explains why Venus has lost water at a much faster rate than previously thought. The research conducted by planetary scientists Michael Chaffin and Eryn Cangi of the University of Colorado Boulder shows that the dissociative recombination of HCO+ can account for nearly twice the amount of water loss compared to previous models.
While the dissociative recombination model offers a compelling explanation for Venus’ missing water, there are still challenges to overcome. Detecting HCO+ in Venus’ atmosphere remains a hurdle, as current probes lack the capability to confirm its presence. However, with the advancement of technology and the prospect of future Venus missions, scientists are optimistic about resolving this lingering uncertainty. As Eryn Cangi aptly puts it, “There haven’t been many missions to Venus.”